As is generally well known, conventional practice of mapping surface currents, which transport floating objects, vessels or pollutants, employs a pair of spaced apart shore-based radar stations that can survey the same oceanic region, but from different vantage points. The data from both stations are combined, in a vector addition sense, to determine the total surface current field. However, due to the cost and complexity of two-radar installations, efforts have been made to map surface currents utilizing a single radar.
U.S. Pat. No. 4,996,533 issued to May et al. discloses the use of a pulsed monostatic radar operating in the HF/VHF range and using a single transmitting antenna with a wide beam width. There is a linear array of antennas, each with its own receiver/digitizer system to sample the complex signal. The summing and phasing of the signals is done in software. The correlation functions are calculated using two successive complex Fourier transforms. The current vectors are measured as a function of range and angle from the radar site, thereby generating the current map.
However, Barrick (1990) proved that this method works only when flow direction is known with respect to the radar beam.
Subsequently, Barrick taught in U.S. Pat. No. 6,590,523 systems and methods for synthesis of total surface current vector maps by fitting normal modes to radar data. This method includes extracting a scalar data set from a radar signal from a radar. Radial velocity components are calculated from the radar signal. These components are fitted to a set of scalar eigenfunctions and eigenvalues to simultaneously solve for the best set of normal modes and the corresponding set of constants. The corresponding set of constants represents a corresponding set of amplitudes. The set of constants and the set of normal modes are used to create a two dimensional vector field used in creating a total vector map.
However, it is believed that Barrick's method is only useful in regions where there are known Eddie currents. It is unclear from Barrick's patent how his methods perform in uniform surface current zones.
Furthermore, both May et al. and Barrick use complex mathematical equations to map surface currents and are limited to short-range system, approximately 50 kilometer range from the radar site.
Therefore, there is a need for a method for determining long-range surface currents from a high frequency single radar station.